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311.
Prior estimates of economic loss from ozone damage to food crops have not allowed for farmer substitution in inputs—and particularly have not allowed for acreage shifts between crops—in response to yield changes. This is a potentially serious problem since benefits from air pollution control legislation may also be estimated without allowing for this direct substitution. This study explores how much acreage shifting might occur between corn, soybeans, and wheat if ozone were reduced to background levels, and how such substitution might affect the estimation of benefits from ozone reduction. 相似文献
312.
K. L. Smith Jr 《Marine Biology》1983,72(3):249-256
Metabolism of two abundant echinoderm species constituting 99.6% of the epibenthic megafauna in the Santa Catalina Basin, off southern California, USA was measured at 1 300 m during the 1979 “Bathyal Expedition”. Specimens of the ophiuroid Ophiophthalmus normani and the holothurian Scotoplanes globosa, collected by the submersible “Alvin”, were individually placed in respirometers, and measured in situ for O2 consumption and ammonium excretion rates. For O. normani, weight-specific O2 consumption rates decreased with increasing weight and were of comparable magnitude to rates of deep-sea and shallow-water ophiuroids; excretion rates were highly variable. Population O2 consumption and excretion rates for O. normani (estimated from size-frequency distribution, abundance, and rate regression equations) were 1 129.28 μl O2 m-2 h-1 and 27.30 nmol NH 4 + m-2 h-1. Weight-specific O2 consumption and ammonium excretion rates of S. globosa decreased with increasing weight and were of comparable magnitude to rases of shallow-water holothurians. Population O2 constimption and excretion rates of S. globosa were 1.38 μl O2 m-2 h-1 and 4.86 nmol NH 4 + m-2 h-1. Combined population O2 consumption rates for O. normani and S. globosa are of comparable magnitude to that of the sediment community and plankton in the benthic boundary layer (sediment and overlying 50 m water column) of the Santa Catalina Basin. 相似文献
313.
Genetic variation in marine teleosts: High variability in habitat specialists and low variability in habitat generalists 总被引:8,自引:0,他引:8
Genetic variation was reviewed in 106 species of marine teleosts. Two heterozygosity estimates were used, one including all protein and enzyme loci and a second excluding the non-enzymatic protein loci. Mean heterozygosities are 0.055±0.036 based on all loci in 106 species and 0.060+0.038 based on enzymatic loci in 89 species. A significant negative correlation was noted between heterozygosity and the proportion of general protein loci included in the estimate. A comparison was made of heterozygosities among taxonomic orders and families, life zones, reproductive mode, geographical range and size. High levels of genetic variation are found in Clupeiformes, Atheriniformes, Pleuronectiformes, temperate pelagic, tropical, intertidal-sublittoral and wide-range species. Low levels of genetic variation are found in Gadiformes, Scorpaeniformes, temperate demersal, polar, and narrowrange species. The most striking differences in heterozygosities are between temperate demersal flatfishes and temperate demersal round fishes. It is suggested that much of the data can be explained by a habitat specialist-generalist model, with high heterozygosities in specialists and low heterozygosities in generalists, but that this is only one of a mosaic of factors which influence genetic variation. 相似文献
314.
P. J. Smith 《Marine Biology》1987,95(4):489-492
The polymorphic enzyme glucosephosphate isomerase (Gpi-2) was studied in muscle tissue from spawning sand flounder, Rhombosolea plebeia, in Wellington Harbour, New Zealand, between April 1984 and June 1986. There was a significant difference in Gpi-2 allele frequencies between early (March-May) and late (June-September) spawners. Pooling equal numbers of early and late spawners produced a significant excess of homozygotes in the 1984 and 1986 samples. This type of partial assortative mating may account for the frequently observed excess of homozygotes in other marine organisms with long spawning seasons. 相似文献
315.
Observations were made on the behavior of nitrate reductase activity in the green alga Ulva fenestrata under controlled light:dark regimes. The activity of nitrate reductase (NR) was examined in response to normal seasonal photoperiods as well as in response to shortened or extended periods of darkness. NR activity exhibits a light-dependent diurnal rhythm under both normal summer and winter photoperiods, with a maximum in the early morning (2 to 2.5 h after the start of illumination). This peak of activity is followed by a lower steady-state level of activity which is sustained throughout the light period. There is a sustained minimal level of activity in darkness. The morning peak in activity is always observed as long as tissue is illuminated, irrespective of the previous light or dark treatments. As such, it appears that nitrate reductase activity in U. fenestrata is under circadian control. There is no major difference in the NR activity pattern between summer and winter plants, except that the peak activity values in winter plants are consistently much higher (5 times) than in summer plants. The study also suggests that illumination prior to the normal start of photoperiod triggers a different set of regulatory mechanisms, indicating that the physiological state of plants is important in dictating the NR activity response to illumination.Please address all correpondence and requests for reprints to G. J. Smith at his present address (Hopkins Marine Station) 相似文献
316.
Giving respondents time to think in contingent valuation studies: A developing country application 总被引:3,自引:0,他引:3
Dale Whittington V. Kerry Smith Apia Okorafor Augustine Okore Jin Long Liu Alexander McPhail 《Journal of Environmental Economics and Management》1992,22(3)
This paper evaluates whether the time given people to think about their responses to CVM valuation questions influences their answers. Our study was conducted in Nigeria as part of an evaluation of rural households' willingness to pay for public taps and private connections to improved drinking water systems. Respondents who were allowed time to evaluate the proposed water system bid significantly less than those who did not have that time. Moreover, this conclusion was upheld regardless of whether the water system was a public tap or a private connection. 相似文献
317.
Molecular association of Cu,Zn, Cd and 210Po in the digestive gland of the squid Nototodarus gouldi 总被引:5,自引:0,他引:5
In July 1985, very fine burrows extending at least to a sediment depth of 50 cm were found in sediments of the Vöring-Plateau, Norwegian continental slope, at depths of 1 261 to 1 969 m. Such burrows have been described from other areas of the oceans, but until now the producers have been unknown. In the box-cores from Vöring-Plateau sipunculans of the genus Golfingia, subgenus Nephasoma, were identified as inhabitants and producers of these Lebensspuren, which correspond with the fossil ichnogenus Trichichnus. 相似文献
318.
Long-term changes in the benthic community on the coastal shelf of Palos Verdes,Southern California 总被引:1,自引:0,他引:1
Between 1972 and 1982, both wastewater discharge and natural perturbations played important roles in directing marine benthic community structure on the Palos Verdes Shelf in Southern California, USA. Community succession was traced along a gradient of eleven 60 m-depth stations extending from the submarine outfalls. Spatial and temporal biological patterns were identified via direct gradient, clustering and principal-coordinates analyses. Species associations which occupied sites distant from the outfalls in the early 1970s gradually became established closer to the diffusers during the decade. The areal extent of outfall impacts shrank, reflecting both improvements in effluent quality and co-occurring beneficial natural events, specifically the short-term settlement of large numbers of the echiuran Listriolobus pelodes. 相似文献
319.
K. L. Smith Jr. 《Marine Biology》1978,47(4):337-347
Benthic community respiration was measured in situ at 9 stations along the Gay Head-Bermuda transect from depths of 40 to 5200 m. Three methods were used; bell jar respirometers, grab respirometers, and free vehicle respirometers. Benthic community respiration rates spanned three orders of magnitude, decreasing from 21.5 ml O2 m-2 h-1 at 40 m in November to 0.02 ml O2 m-2 h-1 at 5200 m. Rates decreased two orders of magnitude between 40 and 1800 m and then significantly declined again between the continental rise (3650 m) and the abyssal plain stations. Predictive equations for benthic community respiration along the transect reflect a strong correlation with depth of water. Of lesser significance are the correlations with water temperature, dissolved oxygen, benthic animal biomass, surface primary productivity and sediment organic matter. Calculations show that annual benthic respiration can utilize 1 to 2% of the surface primary productivity. Of the 2 to 7% organic carbon fixed at the surface which supposedly reaches the bottom, only 15 to 29% is utilized by the benthic community at 2200, 3000, and 3650 m. The energy requirements of other biological components of deep-sea benthic communities, such as benthopelagic and macro-epibenthic animals, not included in these measurements, must also be considered in calculating a balance of carbon.Contribution from Scripps Institution of Oceanography. 相似文献
320.
Respiratory dynamics of the starry flounder Platichthys stellatus in response to low oxygen and high temperature 总被引:1,自引:0,他引:1
Starry flounder (Platichthys stellatus Pallas) were fitted with masks for measurements of ventilation volume and post-gill oxygen tensions, and with arterial and venous cannulae. They were then subjected to periods of low oxygen levels and high temperature. Pre- and post-gill oxygen tension, blood oxygen tension and content, oxygen uptake, and ventilation volume were measured. Effectiveness of gas exchange across the gills, cardiac output, and transfer factor were calculated. A series of blood-oxygen dissociation curves were also constructed at two pH's and temperatures. The data suggest that flounder are able to regulate oxygen uptake down to an environmental oxygen tension of at least 50 mm Hg by increasing ventilation volume and transfer factor while not changing blood flow rate or pattern. Also, the flounder's response to temperature increase is similar to the expected response to exercise, with the exception of an increase in gill diffusion resistance. 相似文献